1. Field of Invention
The present invention relates to a switching power supply. More particularly, the present invention relates to an apparatus used for compensating the transient output voltage undershoot when the load of a power supply is switched from a light load to a heavy load, and for compensating the transient output voltage overshoot when the load of the power supply is switched from a heavy load to a light load, and a power supply using the same.
2. Description of Related Art
As rapid development of various information and communication equipments, the design of a switching power supply with high efficiency has become a kind of knowledge combined with engineering and experience. The switching power supply is used to switch the power in many applications, including computers, illumination converters, and telecommunication equipments. Taking the DC to DC switching power supply as an example, during the short time for the load to be switched from the light load to the heavy load, since the energy of the DC to DC switching power supply cannot be supplied in time, the output voltage is reduced in a very short time, thus causing an undershoot. However, in many applications, a voltage output must be steady, and the problem that the voltage output drops in a very short time must be limited within a tolerable scope.
The USA manufacturer, Intel Corporation, has established a regulation of Voltage Regulator Down (VRD) standard. In the VRD standard, the output voltage of the power supply is regulated following the demand of the CPU.
However, when the modern CPU is operated under a high load, its power consumption is up to hundreds of watts. When the CPU is operated under a low load, its power consumption is generally about 5 Watts. Generally, the core voltage of the modern CPU is approximately between 1V and 2V. Supposing the core voltage of a CPU is 1V, and supposing its power consumption is 100 Watts when being operated under a high load, at this time, the power supply must supply a current of 100 A, and if the CPU is operated under a low load, the power supply is only required to supply a current of, for example, 5 A.
If the CPU is switched from a low load to a high load, the load of the power supply is also switched from a light load to a heavy load, and at this time, the voltage of the power supply will be suddenly dropped. When the output voltage outputted from the power supply is excessively dropped at instant, the CPU will be entered the protection state due to the drop of the core voltage, and thereby the computer is crashed. Furthermore, the CPU may also be damaged. In addition, as for a computer user, it is not acceptable that the computer is crashed when working. When the CPU is switched from operating under a high load into operating under a low load, the load of the power supply is also switched from the heavy load into the light load, and at this time, the voltage of the power supply will be suddenly arisen, which not only causes an additional power consumption of the CPU due to the increase of the core voltage, but also may damage the CPU.